High resiliency (HR) polyurethane foams are open-celled structures known to have excellent physical properties such as low flex fatigue, low flammability and good load bearing characteristics. As such, they find extensive application in the fabrication of cushioning components in the furniture and automotive industries. These foams are produced by reacting high molecular weight polyols which contain a large proportion of primary hydroxyl groups with organic isocyanates and a blowing agent. When the blowing agent in such a formulation is water, it reacts with some of the isocyanate to form carbon dioxide gas for the foaming system. Thus, in order to achieve the low density foams required for automotive applications, for example, HR polyurethane foam compositions have been formulated with more water than earlier systems. These are designated in the art as "high water" HR polyurethane foam formulations and typically employ more than 4 parts by weight of water per 100 parts of the polyol. Foam density obtained from these compositions is generally below 2 lbs./cubic foot and typically in the range of 1.50 to 1.75 lbs./cubic foot.
In the commercial practice of molding polyurethane foam formulations into shaped articles, a mold, typically aluminum, is coated with a release agent before the foam formulation is introduced and subsequently cured in the mold. This procedure allows facile removal of the cured part without attendant tearing or other damage. A large number of cured as well as uncured silicone coatings are known in the art to act as useful release agents in such applications and the cured coatings typically can provide multiple release of up to about 25-30 shaped articles before recoating of the mold with additional release agent is necessary. However, the above described high water HR polyurethane foam formulations are particularly unstable and each of the currently available release agents has at least one shortcoming which makes its use less than satisfactory in such foaming systems.
Thus, for example, Oppliger, Canadian Patent No. 624,114, teaches that cured films of polysiloxane oils or gums act as release coatings in polyurethane foam molding applications. Oppliger does not teach that these films give multiple releases and the examples and the compositions taught in Opplinger in fact do not give multiple releases of molded high water HR polyurethane foam articles.
U.S. Pat. No. 4,244,912 issued to Battice teaches that a composition comprised of vinyl end-blocked polydimethylsiloxane, vinyl group containing polysiloxane resin, polymethylhydrogensiloxane cross-linking agent, and a platinum containing hydrosilation catalyst is useful as a multiple release coating. This coating does allow multiple releases of molded high water HR polyurethane foam articles and does not defoam the surface of such articles. The coating is difficult to recoat, however, because the platinum-catalyzed cure system is inhibited by the polyurethane foam formulations. Therefore, providing new cured coatings over spent coatings is difficult to ensure in practice.
U.S. Pat. No. 4,534,928 issued to Martin teaches multiple release coatings for polyurethane foam molding applications comprised of predominantly hydroxyl terminated polydimethylsiloxanes, trialkoxysilane, metal alkoxides and nonreactive organic solvent. This composition is applied to a mold surface, the solvent is driven off and a cured film is formed which has multiple release properties. The cured coating tends to defoam high water HR polyurethane foam formulations to the extent that a "skin" of increased density forms on the surface of the foamed article where it comes into contact with the release coating. Moreover, the resultant molded articles show serious surface defects.
Lopes et al., in U.S. Pat. No. 4,681,714, Ser. No. 813,886, filed Dec. 27, 1985, and assigned to the assignee of this invention, teach a durable release composition comprising a hydroxyl endblocked polydimethylsiloxane, an alkyltriacetoxysilane, a non-reactive solvent and, optionally, an organometallic catalyst. Cured coatings based on these compositions do provide good multiple release for low water (i.e., less than 4 parts by weight of water per 100 parts of polyol) HR polyurethane foam compositions. When using a high water HR polyurethane foam formulation, however, these coatings result in an unacceptable molded surface characterized by profuse surface defects measuring approximately 3-4 foam cells in depth and 6-10 cells across designated in the art as "pitting."